For controlling weeds, chemical herbicides have been mainly used. However, serious problems including environmental pollution have been arisen in last several years from the excessive use of chemical pesticides and, therefore, development of weed control agents employing no chemical substances and methods for utilizing such weed control agents have been demanded. In particular, microbial pesticides employing pathogenic microorganisms against weeds have been strongly contemplated. Examples of such microbial pesticides, including some commercially available ones which have been registered, are "DeVine" which is a herbicide against Stranglervine (Asclepiadaceae) developed in the United States, "Collego" which is a herbicide against Northern jointvetch (Leguminosae) developed in the United States and "BioMal" which is a herbicide against Round-leaved mallow (Malvacceae) developed in Canada.
"Collego" is usually sold as a set composed of powder containing spores as the effective ingredient and a solution containing sucrose for suspending the powder therein. These two components must be mixed with each other and diluted with water before use, which requires a great deal of labor. In addition, in such a formulation, raising of powder in the air tends to be caused. "DeVine" is sold in the form of a concentrate solution of the microorganism cells. This herbicide also has a defect in that it can not be stored for a long period of time. [Weed Science 34 (Suppl. 1) (1986):15-16]
In recent years, in the United States and Canada, for the purpose of making the microbial herbicides as mentioned above applicable to plowed fields, improving the adhesion properties of the microbial herbicides to the target weeds and imparting moisture retention on leaves of the weed to make it easy for the microbial herbicides to penetrate in host weeds, studies have been made on using a W/O type surfactant (emulsifier) [Weed Technology 5 (1991):442-444]. W/O type surfactants have been mainly used in the fields of cosmetics and foods and are generally commercially available. However, such surfactants have been rarely used in pesticides. When a W/O type surfactant is used, the finished pesticide must be applied with a specially designed spreader, which is disadvantageous in practical use. Further, when lecithin derived from. crude plant oil is used as the W/O type surfactant, problems in quality control of a lecithin product would arise owing to lot-to-lot variation in lecithin content, color variation in the crude oil and malodor of the lecithin product. Therefore, such formulation has not been practically used yet.
On the other hand, in recent years in Japan, microbial herbicides employing pathogenic microorganisms against weeds have also been studied. In particular, the development of microbial herbicides against Echinochloa crus-galli has been advanced. For example, as such microbial herbicides applicable to paddy fields, those employing as effective ingredient Cochliobolus lunatus [Weed Research (1987), 27, 43-47; Japanese Patent Application Laid-open No. 5-284963], Ustilago trichophora [WO93/05656], and Drechslera monoceras (another name of Exserohilum monoceras) [Japanese Patent Application Laid-open Nos. 3-219883, 4-226905, 4-360678, 4-370090, 6-277042, 6-329513, 6-247822, 7-31467, 7-79784 and 8-175917] have been known. It has also been proposed to formulate a herbicide containing a pathogenic microorganism against Echinochloa crus-galli alone or in combination with a base component of a conventional chemical herbicide in the similar manner as those for formulating a conventional chemical herbicide [Japanese Patent Application Laid-open Nos. 4-226905 and 4-360678]. However, these formulations have same forms as those of conventional chemical herbicides. For example, a granular formulation tends to settle on paddy sail in water, so that the pathogenic microorganisms contained in the granular formulation have little chance to adhere onto the leave of Echinochloa crus-galli, resulting in low herbicidal activity. Wettable powders have also been considered to have problems such as uneven spreadability onto the field, raising of powder in the air which is observed when diluted with water upon use, and the like. Furthermore, such wettable powders have not been used as herbicides for paddy fields because of their inconvenience in treatment and handling. Liquid formulations including floable formulations also have disadvantages such as poor storage properties. Oil formulations have also been developed which are designed to spread the pathogenic microorganisms contained therein over water surface [Japanese Patent Application Laid-open No. 6-179243]. However, such oil formulations have a problem in storage since they should be treated as hazardous materials. Furthermore, in such an oil formulation as disclosed in Japanese Patent Application Laid-open No. 6-179243, the dropwise application to a paddy field would be adversely influenced by wind blowing, and therefore, if it is directly splashed and adhered onto the leaf surface of the cultured rice plants, it would damage the rice plants. For controlling weeds (e.g., Echinochloa crus-galli) or insect pests (e.g., water weevil (Lissorhoptrus orvzophilue)) in paddy fields, it has been known that it is effective to attack the weeds or the insect pests on the water surface. In view of this knowledge, water-floating chemical pesticides have been developed [Japanese Patent Application Laid-open No. 5-78204], in which glassy mineral and pumice are used as carriers. However, such carrier materials are not useful for formulation of microbial pesticides since they have poor adhesive property with microorganisms.